Optical proximity correction for phase shifting photolithographic masks

ABSTRACT

A method for producing a computer readable definition of photolithographic mask used to define a target pattern is provided. The phase shift mask patterns include phase shift windows, and the trim mask patterns include trim shapes, which have boundaries defined by such sets of line segments. For a particular pair of phase shift windows used to define a target feature in a target pattern, each of the phase shift windows in the pair can be considered to have a boundary that includes at least one line segment that abuts the target feature. Likewise, a complementary trim shape used in definition of the target feature, for example by including a transmissive region used to clear an unwanted phase transition between the particular pair of phase shift windows, includes at least one line segment that can be considered to abut the target feature. Proximity correction is provided by adjusting the position of the at least one line segment on the boundary of a phase shift windows in said pair which abuts the target feature, and by adjusting the position of the at least one line segment on the boundary of the complementary trim shape which abuts the target feature.

RELATED APPLICATIONS

This application is related to, claims the benefit of priority of, andincorporates by reference, the U.S. Provisional Patent ApplicationSerial No. 60/296,788 filed Jun. 8, 2001 entitled “Phase ConflictResolution for Photolithographic Masks” having inventors ChristophePierrat and Michel Côté and assigned to the assignee of the presentinvention.

This application is related to, claims the benefit of priority of, andincorporates by reference, the U.S. Provisional Patent ApplicationSerial No. 60/304,142 filed Jul. 10, 2001 entitled “Phase ConflictResolution for Photolithographic Masks” having inventors ChristophePierrat and Michel Côté and assigned to the assignee of the presentinvention.

This application is related to, claims the benefit of priority of, andincorporates by reference, the U.S. Provisional Patent ApplicationSerial No. 60/325,689 filed Sep. 28, 2001 entitled “Cost Functions AndGate CD Reduction In Phase Shifting Photolithographic Masks” havinginventors Christophe Pierrat and Michel Côté and assigned to theassignee of the present invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to manufacturing small dimension featuresof objects, such as integrated circuits, using photolithographic masks.More particularly, the present invention relates to phase shift maskingof complex layouts for integrated circuits and similar objects as wellas proximity correction, including but not limited to optical proximitycorrection and etch proximity correction, for the same.

2. Description of Related Art

Phase shift masking has been applied to create small dimension featuresin integrated circuits. Typically the features have been limited toselected elements of the design, which have a small, critical dimension.See, for example, U.S. Pat. No. 5,766,806.

Although manufacturing of small dimension features in integratedcircuits has resulted in improved speed and performance, it is desirableto apply phase shift masking more extensively in the manufacturing ofsuch devices. However, the extension of phase shift masking to morecomplex designs results in a large increase in the complexity of themask layout problem. For example, when laying out phase shift windows ondense designs, phase conflicts will occur. One type of phase conflict isa location in the layout at which two phase shift windows having thesame phase are laid out in proximity to a feature to be exposed by themasks, such as by overlapping of the phase shift windows intended forimplementation of adjacent lines in the exposure pattern. If the phaseshift windows have the same phase, then they do not result in theoptical interference necessary to create the desired feature. Thus, itis necessary to prevent inadvertent layout of phase shift windows inphase conflict near features to be formed in the layer defined by themask.

Another problem involves efficient layout of optical proximitycorrection OPC features, and other proximity correction features. In onesystem provided by the assignee of the present invention, known asiN-Phase 4.0 from Numerical Technologies, Inc., San Jose, Calif., amodel OPC feature for OPC of gate shrink designs is featured, and OPC ofthe phase shift pattern along the gate region to correct for lightimbalance is provided.

In the design of a single integrated circuit, millions of features maybe laid out. The burden on data processing resources for iterativeoperations over such large numbers of features can be huge, and in somecases makes the iterative operation impractical. The layout of phaseshift windows and the assignment phase shift values to such windows,along with the layout of complementary trim mask patterns, for circuitsin which a significant amount of the layout is accomplished by phaseshifting, is one such iterative operation which has been impracticalusing prior art techniques.

Because of these and other complexities, implementation of a phase shiftmasking technology for complex designs will require improvements in theapproach to the design of phase shift masks.

SUMMARY OF THE INVENTION

The present invention provides techniques suitable for use with complexphase shift mask patterns and complementary trim mask patterns, whichallow for improved proximity correction.

Thus, a method for producing a computer readable definition ofphotolithographic mask used to define a target pattern is provided. Forthe purposes of this description, the phase shift mask patterns and trimmask patterns include shapes having boundaries that are defined by setsof line segments. The phase shift mask patterns include phase shiftwindows, and the trim mask patterns include trim shapes, which haveboundaries defined by such sets of line segments. For a particular pairof phase shift windows used to define a target feature in a targetpattern, each of the phase shift windows in the pair can be consideredto have a boundary that includes at least one line segment that abutsthe target feature. Likewise, a complementary trim shape used indefinition of the target feature, for example by including atransmissive region used to clear an unwanted phase transition betweenthe particular pair of phase shift windows, includes at least one linesegment that can be considered to abut the target feature. According tothe present invention, proximity correction is provided by adjusting theposition of the at least one line segment on the boundary of a phaseshift windows in said pair which abuts the target feature, and byadjusting the position of the at least one line segment on the boundaryof the complementary trim shape which abuts the target feature.

In one embodiment, the at least one line segment on the phase shiftwindows is defined by dissecting boundaries of the phase shift windowsin the pair of phase shift windows at dissection points that areselected according to the shape of the phase shift windows. For example,the dissection points are selected so that they occur along the edge ofthe target feature at positions corresponding to corners of the phaseshift windows. In addition, the at least one line segment on the trimshape is selected by dissecting boundaries of the trim shape atdissection points selected according to the shape of the trim shape.Again, for example the dissection points on the trim shape are selectedso that they occur along the edge of the target feature at positionscorresponding to corners of the trim shape.

In another embodiment, the pair of phase shift windows discussed in thepreceding paragraph includes a complementary phase shift window by whicha phase transition is produced that results in formation of at least apart of the target feature. The line segments for the phase shiftwindows in the pair are defined by dissecting a boundary of the phaseshift window at a dissection point at corner of the phase shift windowwhich abuts an edge of the target feature caused by the phasetransition. Likewise, the line segments of the trim shape are defined bydissecting the boundary of the trim shape at dissection points at thecorner of the trim shape which abuts an edge of the target featurecaused by the phase transition.

Another embodiment of the invention provides a method for performingoptical proximity correction for a target feature of integrated circuitlayout. In this embodiment, the layout is accomplished using a fullphase pattern that comprises a first phase shift window and the secondphase shift window. The first and second phase shift windows haverespective sides comprising at least one line segment abutting thetarget feature. A phase transition between the first and second phaseshift windows cause an artifact to be trimmed. For example, the firstand second phase shift windows may abut the sides of intersecting linesegments in the target pattern, and create a phase transition at theinside corner of the intersection that would create an artifact to betrimmed. A trim shape comprising at least one line segment abutting thetarget feature is used to trim the artifact. According to the presentinvention, at least one line segment of the first phase shift window andat least one line segment of the trim shape that abut the target featureare identified. Proximity correction is performed by adjusting thepositions of both the identified at least one line segment of the firstphase shift window and the identified at least one line segment of thetrim shape. Said adjusting includes for example offsetting the at leastone line segment of the phase shift window and the at least one linesegment of the trim shape from adjacent line segments definingboundaries of the features, preferably in a direction which isorthogonal to the adjacent line segments that define boundaries offeatures.

Another embodiment of the invention includes layout a first mask patternincluding phase shift windows having boundaries defined by line segmentsin a first mask layout, and a second mask pattern including trim shapeshaving boundaries defined by line segments in the second mask pattern.In this embodiment, the combination of the first and second maskpatterns is used for defining a target pattern in which at least a partof an exposure feature caused by a phase transition between a pair ofphase shift windows in the first mask pattern is cleared by atransmissive region in a trim shape in the second mask pattern to definea portion of the target feature. Next, the invention includes adjustingthe position of a line segment defining boundaries of the pair of phaseshift windows in the first mask pattern that create said exposurefeature to be cleared by the transmissive region, and the position of aline segment defining boundaries of the transmissive region in thesecond mask layout to provide for proximity correction for the targetfeature. Next, a result of the laying out and adjusting is stored in acomputer readable medium.

In yet another embodiment, these techniques are applied to phase shiftwindows and trim shapes used for definition of inside corners of targetfeatures. In a further embodiment, these techniques are applied to phaseshift windows and trim shapes used for definition of outside corners oftarget features.

According to another aspect of the present invention, a computerreadable definition of the photolithographic mask is provided thatdefine the pattern in a layer to be formed which includes a targetfeature having first and second outside corners form by intersections offirst, second and third edges of the target feature. According to thisembodiment of the invention, a method includes laying out a first maskpattern including phase shift windows and a second mask patternincluding trim shapes, wherein the first and second mask patterns areused in combination for defining the first and second outside corners ofthe target feature. The first mask pattern including first and second ashift windows having opposite phases and abutting the first and secondedges of the target feature near the first outside corner, and the thirdphase shift window having the same phase as the first phase shift windowand abutting the third edge of the feature near the second outsidecorner. A first phase transition occurs between the first and secondpatient windows in a location near the first outside corner and cause anexposure feature tending to extend in a line away from the first outsidecorner. A second phase transition occurs between the second and thirdphase shift windows in a location near the second outside corner, andcauses an exposure feature tending to extend in a line away from thesecond outside corner. The second mask pattern includes a trim shapehaving a first transmissive region corresponding to a location of thefirst phase transition for clearing at least a portion of the exposurefeature caused by the first phase transition such that the first outsidecorner is sharper in a resulting image, and has a second transmissiveregion corresponding to the location of the second phase transition forclearing at least a portion of the exposure feature caused by the secondphase transition such that the second outside corner is sharper in theresulting image. Proximity correction adjustments are applied to one orboth of the first and second mask patterns. The result is stored in acomputer readable medium.

Other aspects of the invention include an article of manufacture thatcomprises a computer readable storage medium with computer readableinstructions stored thereon for executing the layout processes justdescribed. Further, lithographic masks are provided that include one ormore masks having phase shift mask patterns and trim mask patterns laidout as described. Also, a method for manufacturing integrated circuitsis provided based upon use of mask patterns that are laid out asdescribed.

In various embodiments of the invention, the trim mask pattern definesbinary shapes only. In other embodiments, the trim mask pattern includesone or more of tricolor shapes, attenuated phase shift windows, andattenuated opacity shapes.

Further aspects and advantages of the present invention can beunderstood upon review of the figures, the detailed description and theclaims which follow.

BRIEF DESCRIPTION OF THE FIGURES

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request and payment of the necessaryfee.

FIG. 1 is a legend showing symbols that will be used in subsequentfigures.

FIG. 2 shows the placement of dissection and evaluation points on bothphase and trim patterns for a straight line layout.

FIG. 3 shows the placement of dissection and evaluation points on bothphase and trim patterns for an inner corner.

FIG. 4 shows the placement of dissection and evaluation points on bothphase and trim patterns for an outer corner.

FIG. 5 shows the placement of dissection and evaluation points on bothphase and trim patterns for a complex pattern.

FIG. 6 is a process flow diagram for setting up and performing opticalproximity correction (OPC) for a layout.

FIG. 7 shows a corner with the phase shifters separated by a cut priorto OPC correction.

FIG. 8 shows a layout with a corner with a single, uncut, phase shifterprior to OPC.

FIG. 9 shows a layout with a contact defined using phase shifters priorto OPC.

FIG. 10 is a simulation of the uncorrected layout of FIG. 7.

FIG. 11 is a simulation of the uncorrected layout of FIG. 8.

FIG. 12 is a simulation of the uncorrected layout of FIG. 9.

FIG. 13 shows a layout with two contacts, one with a phase conflict andthe other with the conflict removed.

FIG. 14 is a simulation of the uncorrected layout of FIG. 13.

FIG. 15 shows a layout with two copies of feature each defined using adifferent phase shifter arrangement.

FIG. 16 is a simulation of the corrected layout of FIG. 15.

FIG. 17 shows a portion of a complex layout.

FIG. 18 shows the phase shift pattern for the layout of FIG. 17 afterOPC has been performed.

FIG. 19 shows the trim pattern for the layout of FIG. 17.

FIG. 20 shows the simulated exposure for the layout of FIG. 17 using thephase and trim patterns of FIGS. 18-19.

FIG. 21 shows a portion of a complex layout.

FIG. 22 shows the phase shift pattern for the layout of FIG. 21 afterOPC has been performed.

FIG. 23 shows the trim pattern for the layout of FIG. 21.

FIG. 24 shows the simulated exposure for the layout of FIG. 21 using thephase and trim patterns of FIGS. 22-23.

FIG. 25 shows a portion of a layout where critical dimension within aregion has been further reduced.

FIG. 26 shows a portion of the layout of FIG. 25 after the shifterwidths are further adjusted to produce the reduced critical dimensionregion.

DETAILED DESCRIPTION

Overview

Optical proximity correction (OPC) involves modification of one or morelayouts that will be used in the production of a layer of material tocorrect for optical effects of the exposure of a mask in lithographyequipment for integrated circuit (IC) production. (Note, as used herein,the term mask includes the term reticle.)

The OPC process involves adding and removing hammerheads, serifs, andthe like to the pattern (composed of structures and/or features) in alayout so that a mask made from the pattern in the resulting correctedlayout will more accurately produce the desired original, or reference,pattern from the target layout on the finished IC. Proximity correctionfor other artifacts of the lithographic process, including etchproximity effects for example, is also possible using suchmodifications.

More particularly, the application of OPC to layouts designed forproducing substantially all portions of a layout pattern will beconsidered. The techniques described apply to other types of proximitycorrection as well. First, the types of layouts being considered will bediscussed in greater detail. Next, the selection of dissection andevaluation points for OPC on such layouts will be considered in greaterdetail. Then, OPC of corners will be considered in greater detail withreference to the layout of the phase shift layout and phase assignment.Finally, example layouts together with trim masks and sample exposureresults will be considered.

Layouts

In one embodiment of the invention, substantially all portions of apattern in a layout are being defined using a phase shifting mask. Masksfor such layouts are sometimes referred to as “full phase” masks. In oneembodiment, the layouts are defined according to the process describedin U.S. patent application Ser. No. 09/932,239 filed Aug. 17, 2001,entitled “Phase Conflict Resolution for Photolithographic Masks” havinginventors Christophe Pierrat and Michel Côté, and assigned to theassignee of the present invention, which is incorporated herein byreference.

In another embodiment, a phase shifting layout that produces substantialportions of a pattern of an IC using phase shifting comprises a phaseshifting layout where substantially all features for a particular layerare defined using phase shifting. In another embodiment, a phaseshifting layout that produces substantial portions of a pattern of an ICusing phase shifting comprises a layout such that only features that arenon-critical for the binary exposure are non-phase shifted.

In other embodiments, the relevant layout comprises a layout where atleast one of:

eighty percent (80%) of non-memory portions in one layer of material inthe layout;

eighty percent (80%) of a part of the floorplan in one layer ofmaterial;

eighty percent (80%) of cells in a given area;

ninety percent (90%) of a layer of material;

ninety five percent (95%) of a layer of material;

ninety nine percent (99%) of a layer of material;

one hundred percent (100%) of a layer of material;

one hundred percent (100%) of a in a functional unit of the chip (e.g.ALU) in one layer of material;

one hundred percent (100%) of features in a layer of material that arein the critical path of the design;

one hundred percent (100%) of features in a layer of material above orbelow certain dimensions, e.g. all features with a critical dimension 50μm<CD<100 μm;

everything in a layer of material except those features that cannot bephase shifted due to phase conflicts that cannot be resolved;

everything in a layer of material except test structures; and

one hundred percent (100%) of all non-dummy features, e.g. featuresproviding structural support for processing purposes, andnon-electrically functional features in a layer of material

are defined using phase shifting.

In one embodiment, the percentages are computed based on the percentageof edges, or OPC edge segments, defined using phase shifting. Turningbriefly to FIG. 2, the edge between the dissection point 210 and thedissection point 212 is defined by the trim mask while the remainingedges of the feature 200 are defined using the phase shifting mask. Inother embodiments, the percentage is determined by area.

The remainder of this application will consider OPC on layouts meetingone or more of the above criterion.

Dissection and Evaluation Points and OPC Process

The OPC process itself may be a rule based or a model based OPC process,or both. If a rule based process is used, the rules may be constructedthrough examination of the performance of model based OPC processaccording to the methods described herein. The trade off between the twois usually quality (model based generally produces better results) fortime (rule based is generally faster).

The model based OPC process will now be considered in greater detail asfollows. First, some terminology and information about model based OPCwill be discussed. Next, setup and dissections for: a straight line, aninner corner, an outer corner, and a more complex pattern, will beconsidered. Finally, a process flow for model based OPC on layouts wheresubstantially all portions of a pattern in a layout are being definedusing a phase shifting mask will be considered.

Model Based OPC Terminology

Model based OPC involves the simulation of the optical effects of a userselected lithography process to a given layout at evaluation pointsplaced within a pattern of a layout.

In one embodiment, the lithography process is modeled using an opticalmodel generated by the ModelGen(TM) software produced by NumericalTechnologies, Inc., of San Jose, Calif. The ModelGen software allows forthe description of the characteristics of the optical lithography systembeing used including, among other things, the wavelength of light (λ),the numerical aperture (N.A.), the coherency of the light (e.g., σ) foreach exposure, the type of illumination (off-axis, quadrapole, etc.),etc.

That optical model can be calibrated for the particular process andlithographic stepper or scanner by making a test exposure and measuringthe critical dimension (CD) of test features. The calibration can beaccomplished by providing the test measures to the ModelCal(TM) softwareproduced by Numerical Technologies, Inc. of San Jose, Calif. Otherembodiments of the invention can support optical models generated or beused in conjunction with software from tools from Avant! Corporation,Fremont, Calif., and Mentor Graphics Corporation, Wilsonville, Oreg.

Together with an optical model, calibrated or otherwise, OPC parametersare provided for the positioning of dissection and evaluation points bythe OPC process. The OPC parameters include measurements that can begiven as a segment length, e.g. 60 nm, 120 nm, etc. The segment lengthdescribes how far apart, and thus how frequently, or infrequently, linesegments that make up features or structures in the pattern in thelayout are dissected and evaluated. The OPC software may allow differentsegment lengths for different types of features, e.g. outer corner,inner corner, straight line, etc.

In one embodiment, the TROPiC(TM) software, the iN-Phase(TM), theiN-Tandem(TM) software and/or the Photolynx(TM) software from NumericalTechnologies, Inc., are used to provide model based OPC as describedmore fully below. In other embodiments, the OPC process is performedusing software provided by Avant! and/or Mentor Graphics.

FIG. 1 is a legend showing symbols that will be used in subsequentfigures. More specifically, FIG. 1 includes a legend 110. Dissectionpoints in subsequent figures for both the trim pattern and the phaseshifting layer will be shown as an eight cornered “Petronas towers”shape of a square intersected with a rotated square. Dissection pointsfor the trim patterns will be shown as a diamond. Dissection points forthe phase shift pattern will be shown as a square. Evaluation points fortrim layouts will be shown as an X and evaluation points for phaselayouts as plus marks. These symbols will facilitate a betterunderstanding of the placement of dissection and evaluation points usedby embodiments of the invention.

Straight Line Dissection

FIG. 2 shows the placement of dissection and evaluation points on bothphase and trim patterns for a straight line layout. FIG. 2 includes atarget feature 200, a straight line. The feature 200 is an element of atarget layout, which the phase shift mask and trim mask are designed toimplement. This feature 200 presents a target that includes elementsformed by the phase transition between the shifters 202 and 204, and anelement, that is the line end, defined by the trim 206. The shifter 202and the shifter 204 represent opposite phase, light transmissive regionson a phase shifting layout for producing the feature 200. The phaseshifting layout will make use of a dark field mask and the area between,and around, the shifter 202 and the shifter 204 will be non-transmissive(opaque), e.g. chrome, etc.

The binary trim layout includes the trim 206 shown as a dashed line (thedashed outline follows, and is obscured by, the solid line of thefeature 200 along the top edge of the feature 200). The binary trimlayout can be a bright field mask for use in conjunction with the phaseshifting mask to define the feature 200. Opaque areas in the trim maskprotect features of the target layout formed by the phase shift maskthat are part of the target feature. Transmissive areas in the trim maskare used to clear unwanted exposure features caused by the phase shiftmask. Also, transmissive areas are used to refine or delimit featurescaused by the phase shift mask so that they more closely match thetarget layout. For example, transmissive areas in the trim mask are usedto define line ends for lines that are formed using phase transitions inthe phase shift mask.

Turning to OPC of the phase layout. Dissection and evaluation will occurwhere the phase layout abuts the target layout, e.g. the feature 200.FIG. 2 shows a portion of the dissection and evaluation points for theshifter 202 and the shifter 204. The dissection and evaluation pointsare placed along the full length of the edges of the shifters where theshifters abut the feature 200 in some embodiments of the invention; seee.g. FIG. 4 and FIG. 5.

Turning to OPC of the trim layout, the trim 206 (opaque rectangleoverlying feature 200 and portions of shifters 202 and 204) includesdissection and evaluation points where the trim 206 abuts the feature200, e.g. along the top edge of the feature 206. In this example, thedissection points 210, 212 and evaluation point 211 for the trim patternand the phase shift pattern along the top edge of feature 200 are atpositions in the respective patterns that correspond to the samelocation on the target feature. More specifically, in this example, thedissection point 210 and the dissection point 212 are used in definingOPC segments in both layers. However, more generally, the placement ofthe dissection points and evaluation points can be determined forparticular layouts based on the edge segments where the transmissivefeature of the trim pattern abuts the target layout and thedissection/evaluation segment length criterion being used. In thisexample, the trim 206 is used to define an end of the feature 200between the points 210 and 212, and to protect the rest of the feature200 formed by the phase transition between shifters 202 and 204.

Summarizing, according to one embodiment of the invention, the trim andphase shift patterns are dissected only where they abut the original(target) layout. Once the dissection and evaluation points have beenplaced, OPC (and other proximity correction adjustments) can beperformed. The dissection of an inner corner will now be considered.

Inner Corner Dissection

FIG. 3 shows the placement of dissection and evaluation points on bothphase shift patterns and trim patterns for an inner corner. Morespecifically, FIG. 3 includes a feature 300 and shows respectiveportions of the phase shift and trim patterns that will be used todefine the feature 300. The phase shift pattern includes two shifters, ashifter 302 and a shifter 304. Shifters on the opposite side of thefeature 300 that would allow the feature 300 to be completely defined byphase shifting are not shown. One side of the outline of the trim 306 onthe trim pattern in the corner is shown as a dashed line. (Note: thetrim 306 follows, and is obscured by, the boundary of the feature 300 onthe inside corner through points 322, 318, 320. See, e.g. FIG. 19 andFIG. 23 for full examples of the shape of trim patterns.) As in FIG. 2,several dissection and evaluation points are omitted from the figure tofocus on the inner corner area; see FIG. 4 and FIG. 5 for more completeexamples.

The gap between the shifter 302 and the shifter 304 and can also bereferred to as a “cut.” In a dark field phase mask produced from thelayout, this gap will be nontransmissive on the phase shift mask. Thecorresponding trim mask typically includes a transmissive area in theregion of the cut to clear any unwanted exposure caused by the phasetransition between the shifter 302 and the shifter 304. In oneembodiment of the invention, the size and shaping of the cuts on thephase shift mask are designed to support easy mask manufacturabilityand/or satisfaction of design rule checking. In one embodiment, the gapareas make use of 45 degree and ninety degree angles. In anotherembodiment, an inner corner cut is formed by a substantially squareshaped notch with a forty-five (45) degree angle straight line out ofone corner to separate the two shifters. The separation between theshifters along the cut is designed to obey any minimum spacing rules forone or more of mask manufacturability and/or design rule checking.Unless stated otherwise, the cuts and angles shown in the figures willbe at 45 and 90 degrees. Other embodiments of the invention can supporthandling of patterns with features aligned and positioned withnon-Manhattan geometries (e.g. non 45/90 degree angles); however, suchembodiments may make use of shifters and cuts while using Manhattangeometries in the cut shapes to the extent possible.

FIG. 3 highlights several dissection points for the phase shift pattern,more specifically the dissection point 310, the dissection point 312,the dissection point 314, and the dissection point 316 are shown. Thedissection point 314 and the dissection point 316 have been positionedproximate to the junction of the respective shifter 304 and shifter 302and the feature 300. Additionally, the dissection point 310 and thedissection point 312 have been positioned in line with the point (310 aand 312 a, respectively) where the full width of the shifter begins, asshown by the dotted-and-dashed line extending from the dissection pointsto the full width of the respective shifter 304 and shifter 302.However, in some embodiments those dissection points are onlysubstantially inline with the beginning of the full width of theshifter. In other embodiments, those dissection points are further intothe full width portion of the shifter by a small amount, e.g. a fewnanometers.

FIG. 3 shows distinct trim pattern dissection points where the trim 306meets the feature 300, e.g. the dissection point 320 and the dissectionpoint 322. Accordingly, in this embodiment the trim pattern dissectionsegments will run from the dissection point 318 to the dissection point322 and the dissection point 320. This supports differing OPCcorrections for the phase and trim patterns. However, if desired thedissection point 314 and the dissection point 316 can be used in OPC ofthe trim pattern. The dissections for an outer corner will now beconsidered.

Outer Corner Dissection

FIG. 4 shows the placement of dissection and evaluation points on bothphase and trim patterns for an outer corner. Here a feature 400 will bedefined using the shifter 402 and the shifter 404. The outline of thetrim pattern is not explicitly shown; however, several of the dissectionpoints are positioned at the intersection of the trim pattern and thefeature 400. Specifically, contrast dissection point 406 and dissectionpoint 408. Dissection point 406 is positioned where the shifter 404meets the feature 400 while the dissection point 408 is positioned wherethe trim 410 meets the feature 400. As noted, this facilitates differentOPC corrections for the phase and trim patterns. Note also thecorresponding dissection points on the other edge of the corner, notlabeled.

Turning more closely to the bottom portion of the feature 400, threedissection points: the dissection point 420, the dissection point 422,and the dissection point 424, are shown. The dissection point 420 andthe dissection point 424 form an OPC segment along the feature 400 forthe trim pattern. However, because in this example the segment is toosmall relative to the selected OPC parameters, no evaluation point isplaced. The dissection point 422 forms an OPC segment for the phaseshift pattern with the dissection point 422 a further up the feature 400where the shifter 402 and the feature 400 abut in the phase shiftpattern.

Also note that the cut between the shifter 402 and the shifter 404 is ofa similar shape and structure to the cut used between the shifters inFIG. 3. Here, the 45 degree opening stretches out of the upper cornerand towards a square end. The shape of the cut is designed to be designrule checker (DRC) clean and/or to support better maskmanufacturability.

Before turning to a process flow for the OPC process a more complexdissection will now be considered.

Complex Dissection

FIG. 5 shows the placement of dissection and evaluation points on bothphase and trim patterns for a complex pattern including the feature 500.Four shifters, the shifter 502, the shifter 504, the shifter 506, andthe shifter 508 will be used to define the feature 500. As in FIG. 4,the outline of the trim pattern 530 is shown as a dashed line.

FIG. 5 illustrates the use of different dissection points for the phaseand trim pattern at the inside corner cut of the shifter 506 and theshifter 508. FIG. 5 includes separate dissection points for where thetrim pattern meets the original feature. Specifically, FIG. 5 includesthe dissection point 512 and the dissection point 516 for the trimpattern. Note in this example that the trim evaluation point 520 isapproximately midway between the two dissection points. In contrast, thedissection point 514 is at the intersection of the shifter 508 with thefeature 500 and is a phase shift pattern dissection point. Thecorresponding dissection and evaluation points for the shifter 506 areshown without reference numerals, for clarity of illustration. Comparearea around the trim dissection point 516 with the area around thecorner 535 where there is only phase layer. Note the absence ofoverlapping OPC segments since only the phase layer will be adjusted.

Now, a process for performing OPC on layouts where substantially allportions of a pattern in the layout are being defined using a phaseshifting mask will be considered in greater detail.

Process Flow

FIG. 6 is a process flow diagram for setting up and performing opticalproximity correction (OPC) for a layout. This process flow could be usedto setup the OPC dissections seen in FIGS. 2-5 and then to perform theappropriate optical proximity correction. This process is designed foruse on layouts where substantially all portions of a pattern in thelayout are being defined using a phase shifting mask.

The process starts at step 600, as OPC parameters and the layout (phaseshift and trim patterns) to be corrected are loaded. In one embodiment,the OPC parameters include information about the process, e.g. anoptical model, optionally calibrated, is provided at this stage.Additionally, settings such as the frequency of evaluation anddissection for different types of line segments within the layout can beprovided. As noted previously, a model based OPC process is consideredhere, if a rule based OPC is used, the process can be suitably adapted.Loading the layout may involve loading the layout data, e.g. from aGDS-II stream format file, a mask electron beam exposure system (MEBES)format, and/or some other suitable format. In some embodiments, thelayout may be in the memory of the computer system performing theprocess of FIG. 6. For example, if a set of one or more UNIX(R)workstations is being used to perform the process of FIG. 6, the layoutmight be loaded from a network attached storage device into memory.

In some embodiments, the layout loaded at step 600 is a non-phaseshifted layout. In such embodiments, a conversion process may beperformed to convert the input layout to a layout where substantiallyall portions of a pattern in the layout are being defined using a phaseshifting mask prior to continuing the process at step 610. Thisconversion can be performed according to some embodiments as describedin U.S. patent application Ser. No. 09/932,239. In one embodiment, theconversion to a phase shifting layout and the process of FIG. 6 can bothbe performed by a suitable version of the iN-Phase(TM) software fromNumerical Technologies, Inc.

The process continues at step 610 with definition of dissection andevaluation points. In some embodiments step 610 and step 620 operate inparallel. In other embodiments, the order is swapped with step 620performed prior to step 610. In still other embodiments, the steps arecombined into a single step that defines evaluation and trim points forboth layers.

More specifically, the dissection points are placed along edge segmentsof the trim pattern and the phase shift pattern according to the OPCparameters. For example, the OPC parameter might specify that all edgesegments are to be dissected every 120 nm. Other embodiments, mightallow greater selectivity, e.g. for corners, etc. Once the dissectionpoints are placed, the evaluation points can be placed in relation to oron the edge between a pair of dissection points. Returning to FIG. 2, atstep 610, the only portion of trim abutting the feature 200 is the topedge and the length of that edge is such that only the two dissectionpoints can be placed. Then an evaluation point is positioned betweenthose dissection points. As noted, the evaluation point need not beplaced directly on the edge segment and multiple evaluation points couldbe used for a given segment.

In either case, at step 630, optical proximity correction can beperformed. In one embodiment a model based OPC process is used. Inanother embodiment a rule based OPC process is used. In anotherembodiment a hybrid, or mixed mode, OPC process is used. In oneembodiment, the mixed mode OPC process of U.S. patent application Ser.No. 09/514,551 entitled “Method And Apparatus For Mixed-Mode OpticalProximity Correction” filed Feb. 28, 2000, and assigned to the assigneeof this application, is applied to the layout at step 630.

The result, at step 640, is a corrected layout that can be output, e.g.to screen, disk, network attached storage, Internet, etc. The outputlayout might even be directly transmitted to a mask making machine, e.g.input in GDS-II stream format and output in MEBES for use in maskmaking. Other formats may be used in some embodiments of the invention,including proprietary formats used by such companies as Hitachi,Toshiba, Jeol, Leica, etc.

In one embodiment, an instance based (IB) representation of the layoutis used for performing the process of FIG. 6. An IB representation isdescribed more fully in U.S. patent application Ser. No. 09/835,313having a filing date of Apr. 13, 2001 and inventors Chin-Hsen (Michael)Lin, et. al., and assigned to the assignee of the present invention.

Now corner OPC will be considered in greater detail with reference toseveral simulations.

Corner OPC

Turning to FIGS. 7-8, a corner from a layout is shown. Specifically,FIG. 7 shows a layout 700 and FIG. 8 a layout 800. Except for theconfiguration of the phase shifters, the layouts are identical. In thelayout 700, the corner is defined using two opposite phase shiftersseparated by a cut. In the layout 800, a single, uncut phase shifter isused. Neither layout has yet been corrected with OPC.

Simulations of the two layouts are shown in FIGS. 10-11, respectively.The two simulations were performed with identical parameters and acoherency (σ)=0.5. FIG. 10 shows a simulation 1000 of the layout 700 andFIG. 11 shows a simulation 1100 of the layout 800. Note that withoutapplication of OPC, the image contour for the printed image is closer tothe target layout for the layout 700 than the layout 800. (Note, thephase shifters are shown as yellow lines and the trim pattern outline asa dark blue/black line in FIGS. 10-11.)

FIG. 9 further considers the tradeoffs between the number of cuts andthe amount of OPC that will be needed. FIG. 9 illustrates a layout 900for a landing area; the phase shifters defining the contact have beencut at every corner. The result: sharper corner definitions as seen inFIG. 12 showing a simulation 1200 for that uncorrected layout 900.

FIGS. 13-14 further illustrate this with FIG. 13 showing a layout 1300including two landing areas, a left landing area 1310 and a rightlanding area 1320. Again, maximizing the number of cuts, right landingarea 1320, improves corner definition without OPC as shown in FIG. 14that includes the simulation 1400.

However, there can be circumstances where leaving the phase conflict canproduce better results as shown in FIGS. 15-16. As shown, FIG. 15includes the layout 1500 and the left hand copy of the feature includesa phase conflict 1510 where the shifter is not of the appropriate phaseto facilitate the definition of the feature. Contrast that with theright hand copy of the feature where all phase conflicts have beenremoved. The dissection and evaluation points used for both arrangementsare shown as well.

The layout 1500 was dissected and corrected according to the process ofFIG. 6 using parameters of 120 nm/120 nm/120 nm/120 nm indicating theminimum segment length, the maximum segment length, the outer cornersegment length, and the inner corner segment length, respectively. Anoutline of the OPC correction is visible in dark blue/black inside thesimulation 1600 results of FIG. 16. (Both the corrected trim andcorrected phase shift patterns are shown in dark blue/black.)

Here, a layout with a phase conflict produces better results.Accordingly, some embodiments of the invention when defining the phaseshift pattern attempt to maximize the number of cuts for contacts andcorners to reduce the need for OPC correction. In contrast, otherembodiments, may perform simulations for a given feature, structure, orpattern, to select a phase assignment strategy for the given feature.For example, if the OPC parameters are known when the phase shiftinglayout is defined a simulation of the type used to generate FIGS. 10-12,14 and 16 can be used and the critical dimension and corner variancecomputed. However, this approach is likely remain computationallyinfeasible for layouts for real world designs. As such, otherembodiments may use rule or shape tables to select strategies.

For example, a rule table might specify that contacts should receive themaximum number of cuts where possible, while another more specific rulemight identify shapes like the ones of FIG. 15 where a phase conflictshould be maintained.

In some embodiments, one or more cost functions are defined to selectwhen and how to cut the phase shift regions that will define thefeatures of the layout. In some embodiments the cost functions aredesigned to minimize the number of divisions taken, e.g. favor layoutlike the left landing area 1310 over the right landing area 1320.However, some embodiments of the invention use cost functions that takeinto account features and patterns on other layers. For example, if acontact was positioned inside the right landing area 1320, then the costfunction might favor maximizing the number of cuts to improvecontainment of the contact.

Finally, two additional layouts will be considered along with detailedexamples of the phase mask after optical proximity correction and thetrim masks as well.

FURTHER EXAMPLES Example 1

FIG. 17 shows a portion of a layout 1700, the layout 1700 extends pastthe area shown. The layout includes a plurality of features beingdefined using phase shifters. Several aspects of the layout bearmention.

Particularly, the cut 1710 should be contrasted with the cut 1740. Inthe case of the cut 1710, a diagonal cut of the type used for the cut1740 was not possible so a straight line cut was used instead. Also, theadjustment for proximity correction in cut 1710 includes offsetting of aline segment 1711 in a direction orthogonal to adjacent line segment1712 on the phase shift pattern.

In a similar vein, cuts are extended where appropriate, e.g. the cut1720 is an extended corner cut that was made contiguous with a no longerdistinctly visible cut for the endcap.

The finished layout also includes several phase conflicts, two of which,the phase conflict 1750 and the phase conflict 1760, are called out.Another phase conflict also exists near the cut 1730. If the cut 1730had been moved from the bottom right corner of the contact to the upperright corner, the phase conflict in that region would be removed.

In this example, the phase conflicts remaining in the layout will becompensated for—to the extent possible—by OPC according to the processof FIG. 6. In FIG. 18 the layout 1800 for the OPC corrected phase shiftpattern is shown. The OPC was performed only on portions of the phaseshift pattern that abut the location of the target layout.

Similarly, FIG. 19 shows the layout 1900 for the OPC corrected trimlayout.

Finally, FIG. 20 includes the simulation 2000 of the printed image ofthe phase layout 1800 used in combination with the trim layout 1900. Thetarget layout is shown as a dark blue/black line.

Reviewing the simulation 2000, it is apparent that the phase conflictswere not an issue as the features in the layout were defined.Additionally, measurements can be taken to verify whether or not thesimulated printed image meets specifications. In this example it does.

Example 2

FIG. 21 shows a portion of a layout 2100, the layout 2100 extends offthe shown edges. The layout includes a plurality of features beingdefined using phase shifters, shown. The portion of the layout shown hasbeen completely phase shifted without conflicts.

FIGS. 22 and 23 show the phase shift pattern and the trim patternrespectively after OPC has been performed. More specifically, the layout2200 in FIG. 22 illustrates the phase shift pattern after OPC and thelayout 2300 in FIG. 23 illustrates the trim pattern after OPC.

Finally, FIG. 24 includes the simulation 2400 of the printed image ofthe phase layout 2200 used in combination with the trim layout 2300. Thetarget layout is shown as a dark blue/black line.

Reviewing the simulation 2400, it is apparent that the phase conflictswere not an issue because the layout was defined within specification.This can be determined by taking measurements from simulation 2400 andcomparing them against requirements, e.g. acceptable CD variance,electrical connectivity, etc. Additionally, it is useful to note thatthe location of the cut at the corner of the “T” junction is notdetectable, due in part to OPC.

Representative Alternative Embodiments

Embodiments of the invention can operate on layouts where portions ofthe phase shifting layout have been targeted for different criticaldimension sizes. For example, FIG. 25 illustrates a portion of a layoutwhere a feature 2500 is defined using phase shifting by a shifter 2510,a shifter 2520, a shifter 2530, and a shifter 2540. Additionally, aregion 2550 is indicated where the shifter 2510 and the shifter 2540have been modified to produce a smaller critical dimension (CD) than isused for the feature 2500. However, the placement of evaluation anddissection points for the phase shift pattern within the region 2550 isthe same as described above.

Furthermore, the shifter widths abutting the region 2550 can be furtheradjusted to reduce the need for OPC while printing the narrow criticaldimension feature in the region 2550. For example, if necessary theouter edges of the shifters could be made wider than the shifters in thesurrounding region, not shown. Or conversely, the shifter width in theregion 2550 could be made narrower, see FIG. 26. More specifically, FIG.26 includes the feature 2500 defined by the shifter 2520, the shifter2530, a shifter 2610 and a shifter 2640. The shifter 2610 and theshifter 2640 are narrower in the region 2650 where reduced criticaldimension is desired.

The appropriate sizing, e.g. shifter widths, can depend on the availablefield as well as other features surrounding the shifters in the region2550. Also, in some embodiments, a preferred shifter width for reducedcritical dimension features may be selected, e.g. nλ, where n>0.0. Then,to the extent practical based on the layout, the shifter widths inregions like the region 2550 are modified so that the interveningcontrol chrome is a narrower size and the widths correspond to thepreferred shifter width.

In variants of the above embodiments, the target layout may be reducedat critical areas where reduced feature size is desired prior toapplication of the phase shifting process. In such an event, theresultant layout will look similar to FIG. 25 and/or FIG. 26.

Additionally, although the description has primarily focused on examplesof defining a polysilicon, or “poly”, layer within an IC, phase shiftingcan be used to define other layers of material, e.g. interconnects,metal, etc.

Embodiments of the invention can also operate on cuts shaped other thanas described, for example the invention can be applied to cuts where thenotch is a simple diagonal opening without the addition of a squarehead, or base. However, experimental test runs have shown that suchlayouts frequently, but not always, result in OPC corrections inwardtowards the target layout for the first segment. For example, returningto FIG. 3, if the shifter 302 met the dissection point 316 from a 45degree line, then the first OPC segment running to the dissection point312 would typically be biased in towards the feature 300. This may ormay not result in a design rule compliant phase shifter, or trim, shape.Nonetheless, OPC can be performed on such a layout as described above.

In one embodiment, the optical proximity correction (OPC) process for alayout where substantially all of the layout is defined using phaseshifting comprises performing OPC of the binary layer for non-criticalfeatures and performing OPC of the phase shift pattern for criticalfeatures. In each case, OPC is only performed on edges where therespective layer abuts the target layout.

Some embodiments of the invention include computer programs forsimulating stepper exposures using masks to compute appropriate relativedosing between phase and trim/binary exposures. In one embodiment, theICWorkbench(TM) software produced by Numerical Technologies, Inc., SanJose, Calif. is used to simulate the exposure conditions, e.g. as seenin FIG. 10, etc. In other embodiments, computer programs are used toperform optical proximity corrections. In one embodiment, theiN-Phase(TM), iN-Tandem(TM), and/or Photolynx(TM) software programsproduced by Numerical Technologies, Inc., are used to perform theoptical proximity correction processes. In other embodiments, suitabletools from Avant! and/or Mentor Graphics are used in the opticalproximity correction processes. In some embodiments, the computerprograms are stored in computer readable media, e.g. CD-ROM, DVD, etc.In other embodiments, the computer programs are embodied in anelectromagnetic carrier wave. For example, the electromagnetic carrierwave may include the programs being accessed over a network.

As used herein, the term optical lithography refers processes thatinclude the use of visible, ultraviolet, deep ultraviolet, extremeultraviolet, x-ray, e-beam, and other radiation sources for lithographypurposes.

Conclusion

The foregoing description of embodiments of the invention has beenprovided for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations will be apparent. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical application, therebyenabling others to understand the invention for various embodiments andwith various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the following claims.

We claim:
 1. A method for producing a computer readable definition of aphotolithographic mask or masks used to define a target pattern in alayer to be formed using the mask or masks, wherein said patternincludes a target feature; the method comprising: laying out a firstmask pattern including phase shift windows having boundaries defined byline segments in the first mask layout, and a second mask patternincluding trim shapes having boundaries defined by line segments in thesecond mask pattern, wherein in combination the first and second maskpatterns are used for defining said target feature of said targetpattern, a first phase shift window in the first mask pattern beingdefined by a plurality of line segments, including at least one linesegment abutting the target feature and a second phase shift window inthe first mask pattern being defined by a plurality of line segments,including at least one line segment abutting the target feature, and atrim shape including a transmissive region in the second mask patternbeing defined by a plurality of line segments, including at least oneline segment abutting the target feature, in which a shape caused by aphase transition between said first and second phase shift windows inthe first mask pattern is cleared by said transmissive region in saidtrim shape in the second mask pattern; adjusting positions of said atleast one line segment of said first phase shift window in said firstmask pattern, and of said at least one line segment of said trim shapein said second mask layout to provide proximity correction; and storinga result of said laying out and said adjusting in a computer readablemedium.
 2. The method of claim 1, including defining said at least oneline segment in the first mask pattern by dissecting boundaries of saidfirst phase shift window at dissection points selected according to theshape of said first phase shift window, and defining said at least oneline segment in the second mask pattern by dissecting boundaries of saidtrim shape at dissection points selected according to the shape of saidtrim shape.
 3. The method of claim 1, wherein said first mask layoutincludes a pair of phase shift windows is arranged so that each of thephase shift windows in said pair includes a complementary phase shiftwindow by which a phase transition is produced that results in formationof a least a part of said target feature, and including defining saidline segments the first mask pattern by dissecting a boundary of atleast one of the phase shift windows in said pair at a dissection pointat a corner of the at least one of said phase shift windows which abutsan edge of said target feature, and defining line segments in the secondmask pattern by dissecting a boundary of said trim shape at a dissectionpoint at a corner of said trim shape which abuts an edge of said targetfeature.
 4. The method of claim 1, wherein the target pattern comprisesa “full phase” design such that the first mask pattern comprises a “fullphase” mask pattern.
 5. The method of claim 1, wherein the targetpattern is exposed on the layer which can be characterized by one ormore of the following: at least eighty percent (80%) of the non-memoryportions of the pattern are defined by the phase shift pattern; at leasteighty percent (80%) of a part of the floorplan in the pattern isdefined by the phase shift pattern; at least ninety percent (90%) of thepattern is defined by the phase shift pattern; all of the features inthe critical path of the pattern are defined by the phase shift pattern;all features in the pattern except those features that are not phaseshifted due to phase conflicts are defined by the phase shift pattern;everything in the pattern except test structures are defined by thephase shift pattern; and everything in the pattern except dummystructures are defined by the phase shift pattern.
 6. The method ofclaim 1, wherein the target pattern can be characterized by having atleast ninety-five (95%) of the features of the target pattern defined bythe phase shift pattern.
 7. The method of claim 1, wherein said secondmask layout includes one or more of tricolor shapes, attenuated phaseshift windows, and attenuated opacity shapes.
 8. An article ofmanufacture, comprising; a computer readable storage medium, havingstored thereon computer readable instructions for definition of aphotolithographic mask or masks that define a target pattern in a layerto be formed using the mask or masks, wherein said pattern includes atarget feature; the computer readable instructions comprising routinesfor laying out a first mask pattern including phase shift windows havingboundaries defined by line segments in the first mask layout, and asecond mask pattern including trim shapes having boundaries defined byline segments in the second mask pattern, wherein in combination thefirst and second mask patterns are used for defining said target featureof said target pattern, a first phase shift window in the first maskpattern being defined by a plurality of line segments, including atleast one line segment abutting the target feature and a second phaseshift window in the first mask pattern being defined by a plurality ofline segments, including at least one line segment abutting the targetfeature, and a trim shape including a transmissive region in the secondmask pattern being defined by a plurality of line segments, including atleast one line segment abutting the target feature, in which artifactcaused by a phase transition between said first and second phase shiftwindows in the first mask pattern is cleared by said transmissive regionin said trim shape in the second mask pattern; adjusting positions ofsaid at least one line segment of said first phase shift window in saidfirst mask pattern, and of said at least one line segment of said trimshape in said second mask layout to provide proximity correction; andstoring a result of said laying out and said adjusting.
 9. The articleof manufacture of claim 8, wherein the computer readable instructionscomprise routines for defining said at least one line segment in thefirst mask pattern by dissecting boundaries of said first phase shiftwindow at dissection points selected according to the shape of saidfirst phase shift window, and for defining said at least one linesegment in the second mask pattern by dissecting boundaries of said trimshape at dissection points selected according to the shape of said trimshape.
 10. The article of manufacture of claim 8, wherein said firstmask layout includes a pair of phase shift windows is arranged so thateach of the phase shift windows in said pair includes a complementaryphase shift window by which a phase transition is produced that resultsin formation of a least a part of said target feature, and wherein thecomputer readable instructions comprise routines for defining said linesegments the first mask pattern by dissecting a boundary of at least oneof the phase shift windows in said pair at a dissection point at acorner of the at least one of said phase shift windows which abuts anedge of said target feature, and for defining line segments in thesecond mask pattern by dissecting a boundary of said trim shape at adissection point at a corner of said trim shape which abuts an edge ofsaid target feature.
 11. The article of manufacture of claim 8, whereinthe target pattern comprises a “full phase” design such that the firstmask pattern comprises a “full phase” mask pattern.
 12. The article ofmanufacture of claim 8, wherein the target pattern is exposed on thelayer which can be characterized by one or more of the following: atleast eighty percent (80%) of the non-memory portions of the pattern aredefined by the phase shift pattern; at least eighty percent (80%) of apart of the floorplan in the pattern is defined by the phase shiftpattern; at least ninety percent (90%) of the pattern is defined by thephase shift pattern; all of the features in the critical path of thepattern are defined by the phase shift pattern; all features in thepattern except those features that are not phase shifted due to phaseconflicts are defined by the phase shift pattern; everything in thepattern except test structures are defined by the phase shift pattern;and everything in the pattern except dummy structures are defined by thephase shift pattern.
 13. The article of manufacture of claim 8, whereinthe target pattern can be characterized by having at least ninety-five(95%) of the features of the target pattern defined by the phase shiftpattern.
 14. The article of manufacture of claim 8, wherein said secondmask layout includes one or more of tricolor shapes, attenuated phaseshift windows, and attenuated opacity shapes.
 15. A method formanufacturing an integrated circuit having a layer of material having atarget pattern, wherein said target pattern includes a target feature,comprising: laying out a first mask pattern including phase shiftwindows having boundaries defined by line segments in the first masklayout, and a second mask pattern including trim shapes havingboundaries defined by line segments in the second mask pattern, whereinin combination the first and second mask patterns are used for definingsaid target feature of said target pattern, a first phase shift windowin the first mask pattern being defined by a plurality of line segments,including at least one line segment abutting the target feature and asecond phase shift window in the first mask pattern being defined by aplurality of line segments, including at least one line segment abuttingthe target feature, and a trim shape including a transmissive region inthe second mask pattern being defined by a plurality of line segments,including at least one line segment abutting the target feature, inwhich an artifact caused by a phase transition between said first andsecond phase shift windows in the first mask pattern is cleared by saidtransmissive region in said trim shape in the second mask pattern;adjusting positions of said at least one line segment of said firstphase shift window in said first mask pattern, and of said at least oneline segment of said trim shape in said second mask layout to provideproximity correction; producing a computer readable definition of saidfirst and second mask patterns; producing at least one mask using saidcomputer readable definition of said first and second mask layouts; andforming said layer using said at least one mask.
 16. The method of claim15, including defining said at least one line segment in the first maskpattern by dissecting boundaries of said first phase shift window atdissection points selected according to the shape of said first phaseshift window, and defining said at least one line segment in the secondmask pattern by dissecting boundaries of said trim shape at dissectionpoints selected according to the shape of said trim shape.
 17. Themethod of claim 15, wherein said first mask layout includes a pair ofphase shift windows is arranged so that each of the phase shift windowsin said pair includes a complementary phase shift window by which aphase transition is produced that results in formation of a least a partof said target feature, and including defining said line segments thefirst mask pattern by dissecting a boundary of at least one of the phaseshift windows in said pair at a dissection point at a corner of the atleast one of said phase shift windows which abuts an edge of said targetfeature, and defining line segments in the second mask pattern bydissecting a boundary of said trim shape at a dissection point at acorner of said trim shape which abuts an edge of said target feature.18. The method of claim 15, wherein the target pattern comprises a “fullphase” design such that the first mask pattern comprises a “full phase”mask pattern.
 19. The method of claim 15, wherein the target pattern isexposed on the layer which can be characterized by one or more of thefollowing: at least eighty percent (80%) of the non-memory portions ofthe pattern are defined by the phase shift pattern; at least eightypercent (80%) of a part of the floorplan in the pattern is defined bythe phase shift pattern; at least ninety percent (90%) of the pattern isdefined by the phase shift pattern; all of the features in the criticalpath of the pattern are defined by the phase shift pattern; all featuresin the pattern except those features that are not phase shifted due tophase conflicts are defined by the phase shift pattern; everything inthe pattern except test structures are defined by the phase shiftpattern; and everything in the pattern except dummy structures aredefined by the phase shift pattern.
 20. The method of claim 15, whereinthe target pattern can be characterized by having at least ninety-five(95%) of the features of the target pattern defined by the phase shiftpattern.
 21. The method of claim 15, wherein said second mask layout oneor more of tricolor shapes, attenuated phase shift windows, andattenuated opacity shapes.
 22. A lithographic mask set including one ormore masks for use in manufacturing a layer of material having a targetpattern, the target pattern including a target feature, comprising: afirst mask pattern on a mask in said mask set including phase shiftwindows having boundaries defined by line segments in the first masklayout, and a second mask pattern including trim shapes havingboundaries defined by line segments in the second mask pattern, whereinin combination the first and second mask patterns are used for definingsaid target feature of said target pattern, a first phase shift windowin the first mask pattern being defined by a plurality of line segments,including at least one line segment abutting the target feature and asecond phase shift window in the first mask pattern being defined by aplurality of line segments, including at least one line segment abuttingthe target feature, and a trim shape including a transmissive region inthe second mask pattern being defined by a plurality of line segments,including at least one line segment abutting the target feature, inwhich an artifact caused by a phase transition between said first andsecond phase shift windows in the first mask pattern is cleared by saidtransmissive region in said trim shape in the second mask pattern;positions of said at least one line segment of said first phase shiftwindow in said first mask pattern, and of said at least one line segmentof said trim shape in said second mask layout being offset from adjacentline segments defining said phase shift window and said trim shape,respectively, to provide proximity correction.
 23. The mask set of claim22, wherein said first mask layout includes a pair of phase shiftwindows arranged so that each of the phase shift windows in said pairincludes a complementary phase shift window by which a phase transitionis produced that results in formation of a least a part of said targetfeature, and said at least one line segment in the first mask patternhas an end at a corner of the at least one of said phase shift windowswhich abuts an edge of said target feature, and said at least one linesegment in the second mask pattern has an end at a corner of said trimshape which abuts an edge of said target feature.
 24. The mask set ofclaim 22, wherein the target pattern comprises a “full phase” designsuch that the first mask pattern comprises a “full phase” mask pattern.25. The mask set of claim 22, wherein the target pattern is exposed onthe layer which can be characterized by one or more of the following: atleast eighty percent (80%) of the non-memory portions of the pattern aredefined by the phase shift pattern; at least eighty percent (80%) of apart of the floorplan in the pattern is defined by the phase shiftpattern; at least ninety percent (90%) of the pattern is defined by thephase shift pattern; all of the features in the critical path of thepattern are defined by the phase shift pattern; all features in thepattern except those features that are not phase shifted due to phaseconflicts are defined by the phase shift pattern; everything in thepattern except test structures are defined by the phase shift pattern;and everything in the pattern except dummy structures are defined by thephase shift pattern.
 26. The mask set of claim 22, wherein the targetpattern can be characterized by having at least ninety-five (95%) of thefeatures of the target pattern defined by the phase shift pattern. 27.The mask set of claim 22, wherein said second mask layout includes oneor more of tricolor shapes, attenuated phase shift windows, andattenuated opacity shapes.
 28. A method for performing optical proximitycorrection for a target feature of an integrated circuit layout, using afull phase pattern that comprises first and second phase shift windowshaving respective sides comprising at least one line segment abuttingthe target feature, where a phase transition between the first andsecond phase shift window cause an artifact to be trimmed, and a trimshape comprising at least one line segment abutting the target featureand used to trim said artifact, the method comprising: identifying saidat least one line segment of the first phase shift window and said atleast one line segment of the trim shape that abut said target feature;and performing proximity correction to adjust positions of said at leastone line segment of said first phase shift window and said at least oneline segment of the trim shape.
 29. The method of claim 28, wherein saidadjusting includes offsetting said at least one line segment of thephase shift window and said at least one line segment of the trim shapefrom adjacent line segments defining boundaries of said features. 30.The method of claim 28, wherein said adjusting includes offsetting saidat least one line segment of the phase shift window and said at leastone line segment of the trim shape orthogonally from adjacent linesegments defining boundaries of said features.
 31. A method forproducing a computer readable definition of photolithographic masks thatdefine a target pattern in a layer to be formed using the mask, whereinsaid pattern includes a target feature; the method comprising: layingout a first mask pattern including phase shift windows having boundariesdefined by line segments in the first mask layout, and a second maskpattern including trim shapes having boundaries defined by line segmentsin the second mask pattern, wherein in combination the first and secondmask patterns are used for defining said target pattern in which atleast a part of an exposure feature caused by a phase transition betweena pair of phase shift windows in the first mask pattern is cleared by atransmissive region in a trim shape in the second mask pattern to definea portion of said target feature; adjusting positions of a line segmentdefining boundaries of said pair of phase shift windows in said firstmask pattern, and of a line segment defining boundaries of saidtransmissive region in said second mask layout to provide proximitycorrection for said target feature; and storing a result of said layingout and said adjusting in a computer readable medium.
 32. The method ofclaim 31, wherein said adjusting includes adjusting positions of a linesegment defining a portion of a phase shift window in said pair of phaseshift windows in the first mask pattern and of a line segment defining aportion of said transmissive region in the second mask pattern.
 33. Themethod of claim 31, including defining said line segments in the firstmask pattern by dissecting boundaries of at least one of the phase shiftwindows in said pair of phase shift windows at dissection pointsselected according to the shape of said one of the phase shift windows,and defining said line segments in the second mask pattern by dissectingboundaries of said transmissive region and dissection points selectedaccording to the shape of said transmissive region.
 34. The method ofclaim 31, wherein said pair of phase shift windows is arranged so thateach of said phase shift windows in said pair includes a complementaryphase shift window by which a phase transition is produced that resultsin formation of a least a part of said target feature in the layer, andincluding defining said line segments the first mask pattern bydissecting a boundary of at least one of the phase shift windows in saidpair at a dissection point at a corner of the one phase shift windowwhich abuts an edge of said target feature, and defining line segmentsin the second mask pattern by dissecting a boundary of said transmissiveregion at a dissection point at a corner of said transmissive regionwhich abuts an edge of said target feature.
 35. The method of claim 31,wherein said line segments defining boundaries of said first and secondphase shift windows and of said transmissive region have end points atdissection points abutting edges of said target feature selectedaccording to design rules including as arguments the shapes of the firstand second phase shift windows and of said transmissive region.
 36. Themethod of claim 35, wherein said line segments include a first linesegment defining a boundary of a first phase shift window in said pairof phase shift windows, and having an end point at a dissection pointlocated where an end of the first phase shift window abuts an edge ofsaid target feature, and a second line segment defining a boundary ofsaid transmissive region having an end point at a dissection pointlocated where a side of the said transmissive region abuts said edge.37. The method of claim 36, wherein said end point of said first linesegment and said end point of said second line segment overlaysubstantially the same position on said target feature.
 38. The methodof claim 36, wherein said end point of said first line segment and saidend point of said second line segment are positioned at differentlocations on said target feature.
 39. The method of claim 31, whereinthe target pattern comprises a “full phase” design such that the firstmask pattern comprises a “full phase” mask pattern.
 40. The method ofclaim 31, wherein the target pattern is exposed on the layer which canbe characterized by one or more of the following: at least eightypercent (80%) of the non-memory portions of the pattern are defined bythe phase shift pattern; at least eighty percent (80%) of a part of thefloorplan in the pattern is defined by the phase shift pattern; at leastninety percent (90%) of the pattern is defined by the phase shiftpattern; all of the features in the critical path of the pattern aredefined by the phase shift pattern; all features in the pattern exceptthose features that are not phase shifted due to phase conflicts aredefined by the phase shift pattern; everything in the pattern excepttest structures are defined by the phase shift pattern; and everythingin the pattern except dummy structures are defined by the phase shiftpattern.
 41. The method of claim 31, wherein the target pattern can becharacterized by having at least ninety-five (95%) of the features ofthe target pattern defined by the phase shift pattern.
 42. A method forproducing a computer readable definition of photolithographic masks thatdefine a target pattern in a layer to be formed using the mask, whereinsaid pattern includes a target feature having an inside corner formed byan intersection of first and second edges of the target feature; themethod comprising: laying out a first mask pattern including phase shiftwindows having boundaries defined by line segments in the first masklayout, and a second mask pattern including trim shapes havingboundaries defined by line segments in the second mask pattern, whereinthe first and second mask patterns are used in combination for definingthe inside corner of the target feature, the first mask patternincluding first and second phase shift windows having an opposite phasesand abutting the first and second edges of the feature near the insidecorner so that a phase transition occurs between the first and secondphase shift windows in a location near the inside corner, and a secondmask pattern including a trim shape having a transmissive regioncorresponding to the location of the phase for clearing at least aportion of the exposure feature caused by the phase transition;adjusting positions of line segments defining boundaries of said firstand second phase shift windows in said first mask pattern, and of linesegments defining boundaries of said trim shape in said second masklayout to provide proximity correction; and storing a result of saidlaying out and said adjusting in a computer readable medium.
 43. Themethod of claim 42, wherein said line segments defining boundaries ofsaid first and second phase shift windows and of said transmissiveregion have end points near said inside corner at dissection pointsabutting said first and second edges selected according to design rulesincluding as arguments the shapes of the first and second phase shiftwindows and of said transmissive region.
 44. The method of claim 42,wherein said line segments include a first line segment defining aboundary of said first phase shift window having an end point at adissection point located where an end of the first phase shift windowadjacent said inside corner abuts said first edge, and a second linesegment defining a boundary of said transmissive region having an endpoint at a dissection point located where a side of the saidtransmissive region abuts said first edge.
 45. The method of claim 44,wherein said end point of said first line segment and said end point ofsaid second line segment overly substantially the same position on saidtarget feature.
 46. The method of claim 44, wherein said end point ofsaid first line segment and said end point of said second line segmentare positioned at different locations on said target feature.
 47. Amethod for producing a computer readable definition of photolithographicmasks that define a target pattern in a layer to be formed using themask, wherein said pattern includes a target feature having an outsidecorner formed by an intersection of first and second edges of the targetfeature; the method comprising: laying out a first mask patternincluding phase shift windows having boundaries defined by line segmentsin the first mask layout, and a second mask pattern including trimshapes having boundaries defined by line segments in the second maskpattern, wherein the first and second mask patterns are used incombination for defining the outside corner of the target feature, thefirst mask pattern including first and second phase shift windows havingan opposite phases and abutting the first and second edges of thefeature near the outside corner so that a phase transition occursbetween the first and second phase shift windows in a location near theoutside corner, and a second mask pattern including a trim shape havinga transmissive region corresponding to the location of the phase forclearing at least a portion of the exposure feature caused by the phasetransition; adjusting positions of line segments defining boundaries ofsaid first and second phase shift windows in said first mask pattern,and of line segments defining boundaries of said trim shape in saidsecond mask layout to provide proximity correction; and storing a resultof said laying out and said adjusting in a computer readable medium. 48.The method of claim 47, wherein said line segments defining boundariesof said first and second phase shift windows and of said transmissiveregion have end points near said inside corner at dissection pointsabutting said first and second edges selected according to design rulesincluding as arguments the shapes of the first and second phase shiftwindows and of said transmissive region.
 49. The method of claim 47,wherein said line segments include a first line segment defining aboundary of said first phase shift window having an end point at adissection point located where an end of the first phase shift windowadjacent said inside corner abuts said first edge, and a second linesegment defining a boundary of said transmissive region having an endpoint at a dissection point located where a side of the saidtransmissive region abuts said first edge.
 50. The method of claim 49,wherein said end point of said first line segment and said end point ofsaid second line segment overly substantially the same position on saidtarget feature.
 51. The method of claim 49, wherein said end point ofsaid first line segment and said end point of said second line segmentare positioned at different locations on said target feature.
 52. Amethod for producing a computer readable definition of photolithographicmasks that define a target pattern in a layer to be formed using themask, wherein said pattern includes a target feature having first andsecond outside corners formed by intersection of first, second and thirdedges of the target feature; the method comprising: laying out a firstmask pattern including phase shift windows having boundaries defined byline segments in the first mask layout, and a second mask patternincluding trim shapes having boundaries defined by line segments in thesecond mask pattern, wherein the first and second mask patterns are usedin combination for defining the first and second outside corners of thetarget feature, the first mask pattern including first and second phaseshift windows having an opposite phases and abutting the first andsecond edges of the feature near the first outside corner and a thirdphase shift window having the same phase as the first phase shift windowand abutting the third edge of the feature near the second outsidecorner, so that a first phase transition occurs between the first andsecond phase shift windows in a location near the first outside cornerwhich causes an exposures feature tending to extend a line away fromsaid first outside corner, and a second phase transition occurs betweenthe second and third phase shift windows in a location near the secondoutside corner which causes an exposure feature tending to extend a lineaway from said second outside corner, and a second mask patternincluding a trim shape having a first transmissive region correspondingto the location of the first phase transition for clearing at least aportion of the exposure feature caused by the first phase transitionsuch that said first outside corner is sharper in a resulting image, andhaving a second transmissive region corresponding to the location of thesecond phase transition for clearing at least a portion of the exposurefeature caused by the second phase transition such that said secondoutside corner is sharper in the resulting image; providing proximitycorrection adjustments to one or both of the first and second maskpatterns; and storing a result of said laying out and said adjusting ina computer readable medium.
 53. The method of claim 52, wherein saidproviding proximity correction includes adjusting positions of one ormore of the line segments defining boundaries of said first, second andthird phase shift windows in said first mask pattern, and of one or moreof the line segments defining boundaries of said first and secondtransmissive region in the trim shape in said second mask layout.